Formation of solid layers on substrates

ABSTRACT

Disclosed is a method of forming on the surface of a substrate a first solid layer which is suitable for activating a chemical reaction to form a second layer thereon, the method comprising the steps of: applying to the surface of the substrate a first liquid comprising a curable composition and an activator for the second layer-forming chemical reaction; and curing the curable composition, thereby forming a first solid layer adhered to the surface of the substrate, capable of activating the second layer-forming chemical reaction. A second layer can then be formed on the substrate by bringing into contact with the first solid layer a second fluid comprising components of a second layer-forming chemical reaction, activated by the activator, thereby causing a second layer to be formed on the first solid layer.

FIELD OF THE INVENTION

The invention relates to formation of layers on substrates,particularly, but not exclusively, the formation of conductive metalregions on substrates by the reduction of metal ions.

BACKGROUND TO THE INVENTION

There are numerous industrial applications in which it is desirable toform a solid layer of a material on the surface of a substrate. Forexample, it is desirable to form a conductive metal layer inapplications as diverse as the manufacture of printed circuit boards,aerials, and antennae such as those found in mobile telephones, radiofrequency identification devices (RFIDs), smart cards, contacts forbatteries and power supplies, arrays of contacts for flat screentechnologies (liquid crystal displays, light emitting polymer displaysand the like), electrodes for biological and electrochemical sensors,smart textiles and decorative features.

In this specification, unless the context requires otherwise, theadjective solid, in the context of a solid layer, or solid substrate,refers to being in the solid (rather than liquid or gas) phase ofmatter. A solid layer or substrate may be plastic, elastic, resilient,rigid, gelatinous, permeable or have any other property consistent withbeing solid phase.

In some of these applications, the solid layer that is formed covers thesurface. In other applications, the solid layer is patterned, and theaccuracy and fineness of detail of the pattern can be important. Forexample, printed circuit boards may have intricate patterns of copperconductive tracks. Accuracy and fineness of detail is important indetermining the extent of miniaturisation possible on such printedcircuit boards, and the reliability of the electronic circuits builtthereon.

Some methods of forming a solid layer on a surface of a substraterequire a catalyst, or other activator. For example, the electrolessplating process is a solution chemistry plating technique which has beenused for many years to apply a conductive metal coating layer to asubstrate surface, which can be flat or shaped. In the electrolessprocess, a substrate is immersed in a succession of baths in turn.

An example of the electroless process used to form a copper layer on thesurface of a substrate would be as follows:

Firstly, a plastics substrate is etched in a chromic acid/concentratedsulphuric acid bath at 68±2° C. to microscopically etch the surface ofthe plastics substrate, ensuring good adhesion of the copper to thesurface of the plastics substrate.

Secondly, any hexavalent chromic species left on the plastics substanceare neutralised in a bath comprising approximately 30% concentratedhydrochloric acid at around 50° C. The plastics substrate is then addedto a third bath in which an activator is added to prepare the plasticssubstrate surface to absorb the catalyst in the next step. This thirdbath is typically approximately 30% concentrated hydrochloric acid, atroom temperature.

Next, the plastics substrate is dipped into a fourth bath, whichincludes a dilute solution of a palladium colloid along with tin salts.A colloid deposits on the surface of the plastics material to catalysethe deposition of copper in the subsequent plating steps. This bathincludes a high proportion of tin salts, approximately 30% concentratedhydrochloric acid, and is operated at room temperature.

The fifth bath into which the plastics substrate is dipped includes anaccelerator which activates the absorbed palladium, improving the speedand uniformity of deposition. Accelerator baths include around 30%concentrated hydrochloric acid.

Finally, the activated plastics substrate is dipped into a sixth bathincluding a plating solution which, catalysed by the palladium colloidon the plastics substrate, causes copper to deposit onto areas of theplastics substrate which were coated with the catalyst. The platingsolution includes a copper salt, formaldehyde as a reducing agent, andsodium hydroxide to activate the formaldehyde. The composition of theplating solution must be carefully temperature controlled, with atemperature of 45±2° C. being appropriate for some commerciallyapplicable compositions.

In the above example chemistry, the catalyst is required for formationof the copper layer, and the acid pre-treatment step is important as ithelps the resulting metal layer adhere to the substrate.

Various alternatives to this chemistry are known.

For example, WO 2004/068389 describes a method of forming a conductivemetal region on a substrate, comprising depositing on the substrate asolution of a metal ion, and depositing on the substrate a solution of areducing agent, such that the metal ion and the reducing agent reacttogether in a reaction solution to form a conductive metal region on thesubstrate. In some embodiments, a catalyst or other activator isrequired to start the reaction which forms the conductive metal region.In general, a catalyst is applied to a substrate surface, which is thenbrought into contact with the chemical composition which reacts,catalysed by the catalyst, to deposit a metal on the surface of thesubstrate.

It is known to deposit on a substrate, e.g by inkjet printing, acatalyst for a metal-forming reaction, with the catalyst applied in asolution containing a polymeric binder. See, for example, WO 02/099162which discloses use of binders such as ethyl cellulose.

U.S. Pat. No. 6,495,456 discloses formation of electrodes on a chipsubstrate by a process that involves applying a photo-active catalystliquid (of unspecified composition) to a chip substrate, irradiating thesubstrate with light to activate irradiated portions of the liquid(possibly selectively, e.g. using a mask) and then using electrolessplating to form metal on the activated portions.

It is known to use ultra violet radiation and other means to reducepalladium acetate deposited on a substrate to palladium metal, followedby electroless plating of copper. Reduction may be performedselectively, by use of a contact mask, to produce patterned catalyst.Alternatively, palladium produced by infra red treatment may bepatterned by excimer laser ablation using a metal contact mask. SeeZhang et al “VUV light-induced decomposition of palladium acetate filmsfor electroless copper plating” Applied Surface Science 109/110 (1997)487-492 and Esrom “Past selective metal deposition on polymers by usingIR and excimer VUV photons” Applied Surface Science 168 (2000) 1-4.

U.S. Pat. No. 3,900,320 discloses a process for metallizing a plastic orceramic base. A pre-plate solution comprising a compound of catalyticmetal, such as a palladium salt, binder material such as one or morepolymers and solvent are coated on the base and dried so as to form athin polymer layer of about 20 Angstrom to about 3000 Angstrom thickwhich may thereafter be directly plated by contact with an electrolessplating solution. The pre-plate solution has specified viscositycharacteristics and specified high concentration levels of catalyticmetal compound. A photosensitive polymer former can be used as acomponent of the pre-plate solution specifically for photographicallydeveloping a plateable pattern on a substrate such as a circuit board,printing plate or the like.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a method of forming,on the surface of a substrate, a first solid layer which is capable ofactivating a chemical reaction to form a second layer thereon, themethod comprising bringing into contact the substrate surface and afirst liquid comprising a curable composition and an activator for saidsecond layer-forming chemical reaction; and curing the curablecomposition to increase adhesion of the material to the surface of thesubstrate, thereby forming a first solid layer adhered to the surface ofthe substrate, capable of activating said second layer-forming chemicalreaction after contact with a second fluid.

A curable composition is one which can undergo a chemical changeresulting in hardening, preferably solidification. The hardening processimproves adhesion of the material and results in formation of a solidlayer (the first solid layer), that may be rigid, plastic, elastic,resilient, gelatinous, permeable or have any other property consistentwith being in the solid phase, as opposed to liquid or gas. The solidlayer may include regions in liquid or gaseous form.

The curable composition is such that the resulting first solid layeradheres to the substrate, and so is selected having regard to thesubstrate. Adhesion can arise through chemical bonding, physicalbonding, mechanical bonding or a mixture thereof. Use of a curablecomposition can result in improved adhesion to a wider variety ofdifferent substrates than is possible with non-curable catalyticsolutions of the prior art.

The curable composition is brought into contact with the substratesurface while the composition is in liquid form, and is subsequentlycured. Curing typically takes place while the curable composition isstill in liquid form, although the curable composition may instead beconverted to solid form, e.g. by drying, prior to curing.

The activator is typically incorporated in the first solid layer,whether by entrapment, immobilisation or other means, and is typicallydispersed throughout the first solid layer within a matrix formed by thecured composition. The activator is thus adhered with respect to thesubstrate by virtue of its inclusion in the first layer.

The curable composition typically comprises one or more componentchemicals which can undergo a reaction resulting in hardening,preferably solidification.

Preferably, the curable composition comprises one or more monomersand/or oligomers which can polymerise and/or cross-link in use, therebyhardening and forming a solid layer. Preferably, the resulting productforms a matrix, typically a polymer matrix, which includes theactivator. A curable composition including at least some oligomers willoften have lower toxicity than if only monomers were included. Thepresence of at least some oligomers can also result in production of afirst layer having improved physical properties such as flexibility,hardness and abrasion-resistance.

The curable composition is curable in response to appropriate curingconditions. For example, the composition may be curable in response to astimulus, such as electromagnetic radiation of a particular wavelengthband (e.g. ultra-violet, blue, microwaves, infra-red), electron beams,or heat. The composition could instead be curable in response toappropriate chemical conditions, particularly the presence of a chemicalcuring agent or hardener: in this case a “two pack” approach may beadopted, with one chemical component applied in the first liquid and asecond chemical component separately applied (simultaneously orsubsequently). As a further possibility the composition may be curablein response to the presence of species such as moisture or air.Preferably, the curable composition is selected to undergo a reactionresponsive to one or more of the above stimuli. An ultra-violet curablecomposition is currently preferred.

It is preferred to use a first liquid such that no significant orsubstantial heating is required. This means that the method of theinvention can be used with a wide range of substrates, includingheat-sensitive plastics materials. In particular, it is preferred thatthe first layer is formed at temperatures below about 300° C. (allowingthe use of polyimide substrates), desirably below about 200° C.(allowing the use of polyester substrates such as Teonex (Teonex is aTrade Mark)), more desirably below about 100° C. (allowing use of a widerange of themoplastic substrates), yet more desirably below about 50° C.(allowing use of low Tg substrates) and possibly at room temperature,avoiding the need for heating. Heating, if required, is only applied fora relatively short time, typically less than 15 minutes and preferablyless than about 2 minutes for processing efficiency.

Typically, the curable composition comprises one or more monomers and/oroligomers which can form a polymer, and an initiator which starts apolymerisation reaction responsive to a stimulus, as discussed above.Suitable initiators are well known to those skilled in the art. Forexample, benzoyl peroxide, lauryol peroxide,azobis-(1-hydroxycyclohexane) or AIBN (2,2′-azobisisobultyronitile) (allfrom Polysciences, Inc., USA) can be included to initiate apolymerisation reaction responsive to heat. Darocur 1173(2-hydroxy-2-methyl-1-phenyl-propan-1-one), Irgacure 184(1-hydroxy-cyclohexylphenyl-ketone), Irgacure 369(2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1), Irgacure651 (2,2-dimethoxy-1, 2-diphenylethan-1-one), Irgacure 2959(1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one),Irgacure 819 and Irgacure 1700 (Darocur and Irgacure are Trade Marks)are examples of UV photo-intiators, available from Ciba SpecialityChemicals, Manchester, UK and Basel, Switzerland. Typically, suchinitiators generate free radicals responsive to a stimulus. Other curingprocesses can be used, such as cationic curing of materials such asepoxys, vinyl ethers and vinyl esters, where an initiator generatescations responsive to a stimulus.

Conveniently, the monomers and/or oligomers are those known from thefield of UV curable inks, or other curable inks, proposed for inkjetprinting of curable inks. Suitable UV-curable materials includeacrylates and methacrylates, particularly those included in thefollowing list classified by the number of cross-linkable functionalgroups:

Monofunctional

-   Isobornylacrylate (IBOA), e.g. as SR506D-   Octyl decyl acrylate (ODA), e.g. as SR484-   Caprolactone acrylate, e.g. as SR495-   Lauryl acrylate, e.g. as SR335    Difunctional-   Tripropylene glycol diacrylate (TPGDA), e.g. as Actilane 424-   1,6-hexanediol diacrylate (HDDA), e.g. as Actilane 425-   Dipropylene glycol diacrylate (DPGDA), e.g. as SR508-   Propoxylated(2) neopentyl glycol diacrylate (PONPGDA), e.g. as    SR9003-   Tricyclodecanedimethanol diacrylate (TCDDMDA), e.g. as SR833S-   Polyethylene glycol 400 diacrylate (PEG400DA), e.g. as SR344    Trifunctional-   Trimethylol propane triacrylate (TMPTA), e.g. as Actilane 431-   Ethoxylated(3) trimethylol propane triacrylate, e.g. as SR454-   Ethoxylated(6) trimethylol propane triacrylate, e.g. as SR499    Tetrafunctional-   Actilane 505 (a tetrafunctional polyester acrylate oligomer)-   Ethoxylated pentaerythritol tetraacrylate (PPTTA), e.g. as Actilane    440-   Ditrimethylolpropane tetraacrylate (di TMPTA), e.g. as Actilane 441    Hexafunctional-   Dipentaerythritol hexaacrylate (DPHA), e.g. as Actilane 450

The Actilane range is available from Akzo Nobel, The Netherlands.Actilane is a Trade Mark.

The SR range is available from Sartomer, USA.

All of the above acrylates cure in response to free radicals, e.g.generated from an initiator such as Irgacure 819 and Irgacure 1700. Allof the above acrylates are in the form of liquids, although it isinstead possible to use solid monomers and/or oligomers.

It is preferred that some (but not all) of the monomers and/or oligomershave at least 3 cross-linkable functional groups, e.g. being selectedfrom the trifunctional, tetrafunctional and hexafunctional materialslisted above. Use of such materials results in production of polymersthat are more highly cross-linked than polymers formed from monomersand/or oligomers with fewer cross-linkable functional groups, and canprovide a stronger, more robust film with better adhesion to thesubstrate. Too high a proportion of such highly cross-linkable monomersand/or oligomers (having at least 3 cross-linkable functional groups)would, however, tend to form a brittle surface and so should be avoided.In addition, use of too high a proportion of such highly cross-linkablematerials would tend to produce a curable composition of too highviscosity to be suited to inkjet printing.

In general, the higher the number of cross-linkable functional groups,the higher the viscosity of the monomer/oligomer and so the smallerproportion of the monomer/oligomer it is appropriate to use. As anapproximate guide, trifunctional materials should not exceed about 75%by weight of the total monomer/oligomer content of the first liquid,tetrafunctional materials should not exceed about 35% by weight of thetotal monomer/oligomer content or the first liquid, and hexafunctionalmaterials should not exceed about 10% by weight of the totalmonomer/oligomer content of the first liquid.

The method conveniently includes formation of the second layer on thefirst solid layer. The method thus preferably further comprises bringinginto contact the first solid layer and a second fluid that comprises oneor more reagents for chemical reaction, activated by the activator, toform the second layer. The second fluid contacts the activator in thefirst layer, and reacts to form the second layer on the first solidlayer.

The first solid layer need not necessarily finish caring before thesecond fluid is applied.

The second layer of material is typically solid and is conveniently aconductive metal layer, which may be formed by a variety of differentprocesses involving the activator in the first layer. The processestypically involve the reduction of metal ions, and include electrolessplating, as referred to above, and the process disclosed in WO2004/068389.

The improved adhesion of the first layer to the substrate surface madepossible by the invention, as noted above, results in improved adhesionof such a conductive metal layer, and makes it possible to produce athicker layer of metal, e.g. copper, without blistering or peeling ofthe layer from the substrate.

As the activator is located in a layer on the surface of the substrate,the second reaction, e.g. metallisation, will generally occur on or inthe first layer in preference to reaction, e.g. the formation of fineparticles of metal, in the second fluid.

The second fluid may be in the form of one or more components, that maybe applied to the first solid layer simultaneously or sequentially.

The first layer need not be directly adhered to the substrate surface:there may be one or more intervening layers. Further, the second layerneed not be the top or final layer: one or more further layers may beformed thereon.

The method of the invention allows greater choice of substrate for agiven second layer, and vice versa, than would otherwise be possible. Byselecting an appropriate first liquid, such that the first solid layeradheres well to the substrate and the second layer adheres well to thefirst solid layer, the second layer may in some cases be more securelyaffixed with respect to the substrate than if the second solid layerwere adhered directly to the substrate. This can allow a greater choiceof substrate for a given second layer and/or allows a thicker secondlayer to be formed than would be the case if the activator were appliedby a different technique.

The activator is preferably a catalyst, such as palladium for catalysinga metallisation reaction. However, the activator could instead comprisea chemical species which can activate the second layer forming chemicalreaction, but is consumed or reacts in the process, and so is notstrictly speaking a catalyst.

The activator may alternatively comprise a reagent, or a plurality ofreagents which, when brought into contact with a second fluid comprisingcomponents (preferably other components) of a second solid-layer-formingchemical reaction, undergo a chemical reaction leading to formation of asecond layer on the first solid layer.

The activator may be applied in precursor form. In this case, the methodmay include the erter step of chemically converting the one or moreprecursor reagents to an active or catalytic form. For example,palladium acetate may be reduced in situ by a subsequently appliedreducing agent solution, forming palladium metal which can catalysedeposition of metal thereon when an appropriate second fluid is applied.

The first solid layer may coat most or all of the entire substratesurface. Alternatively, the first solid layer may be formed on thesubstrate according to a pattern. This may be achieved in several ways.For example, the first liquid may be deposited according to a pattern,e.g. by printing in the desired pattern, particularly by inkjetprinting. Alternatively, the first solid layer may be patterned afterthe first liquid has been deposited; for example, the first liquid maybe applied extensively across the substrate, selectively cured accordingto a pattern and uncured liquid may then be removed. Selective curingaccording to a pattern can be achieved by use of a mask, such as ashadow mask for liquid or solid layers or a contact mask for solidlayers, to limit exposure to a stimulus as discussed above, e.g. UVradiation. Laser writing (using a laser of appropriate wavelength for aparticular initiator) and electron beam writing can also be used. Withelectron beam writing, a photoinitiator is not required, and thisapproach can be used to create patterns with very fine features, of theorder of 10 nm. As a further possibility, when using chemical curing, acuring agent or hardener may be selectively applied according to adesired pattern. In all cases, excess (uncured) material may be removedby techniques including washing, spraying or immersion in suitablereagents such as an acid, alkali or solvent or by physical means such asuse of an air knife.

Thus, the use of a curable composition can allow patterning to an extentwhich would not be possible were the activator deposited on thesubstrate as a liquid which remained soft and flowed.

The first liquid can be applied extensively to a substrate surface by awide range of possible techniques, including using printing, dipping,spraying and spinning techniques such as jet printing, inkjet printing,spin coating, dip coating, spray coating, aerosol spraying, rollercoating, curtain coating, screen printing, litho printing, flexoprinting, gravure printing and pad printing, or by any other liquidapplication technique.

Preferably, the first liquid is brought into contact with the substrateby a deposition process, for example a printing process. Preferably, thedeposition process is a non-contact process that is preferably digitale.g. inkjet printing. The first liquid is preferably applied as a singleliquid, e.g. by inkjet printing from a single liquid reservoir.

Printing processes typically result in production of a first solid layerhaving a thickness greater than 300 nm and possibly significantlythicker.

The first liquid is typically in the form of a solution, preferably apartially or entirely non-aqueous solution, but may alternatively be inthe form of a suspension or dispersion with one or more components insolid or colloidal form, or an emulsion. Different ingredients of thefirst liquid may be present in different forms. The first liquidgenerally includes a carrier liquid (which may function as a solvente.g. for the activator), which is preferably partially or entirelynon-aqueous. Preferred non-aqueous liquids are discussed below. Thecarrier liquid may be constituted by one or more curable monomers and/oroligomers, e.g. as discussed above, if in liquid form, or may beconstituted by a separate liquid (not part of the curable composition)performing a carrier function only.

The second fluid is preferably in liquid form, and so is a secondliquid.

The second liquid may be in the form of a solution, preferably anaqueous solution, but may alternatively be in the form of a suspensionor dispersion with one or more components in solid or colloidal form, oran emulsion. The second liquid thus generally includes a carrier liquid(which may function as a solvent). The carrier liquid of the secondliquid preferably comprises water.

The first liquid desirably includes a carrier liquid that issufficiently aggressive to the substrate to allow the first liquid topenetrate therein, with the carrier liquid partially dissolving orotherwise permeating into the substrate, increasing adhesion of thefirst solid layer to the substrate, and thus also increasing theadhesion of the second layer to the substrate (via the first solidlayer).

The first liquid and the second liquid preferably comprise differentcarrier liquids. This allows the carrier liquid of the first liquid tobe selected to be appropriate for the formation of the first layer andthe adhesion of the first layer to the substrate, whilst the carrierliquid of the second liquid can be selected to be appropriate for theformation of the second layer. Preferably, the carrier liquid of thesecond liquid is water. Thus, aqueous metallisation chemistry and anon-aqueous first stage can be utilised in different steps of the sameprocess. Preferably, the carrier liquid of the first liquid is partiallyor entirely non-aqueous.

Typically, print quality and adhesion are governed predominantly by theproperties of the first liquid and the first solid layer which it forms.Thus, to some extent, the invention allows the first liquid to beselected dependent on the patterning quality required and the secondfluid to be selected dependent on the desired properties of the secondlayer. This can allow greater flexibility in designing appropriate firstliquid and second fluid chemistries for a particular application.

The first liquid may be selected to have improved wetting properties onone or more substrates as compared with those of the second fluid. Thisallows more accurate and precise patterning than if the first liquid wasapplied from the same carrier liquid (e.g. water) as the second fluid,with fine features and better edge definition being possible. There willtypically be less bleed and feathering of the first liquid than ifactivator were applied to the surface by a different technique using acarrier with poorer wetting properties. Improved wetting propertiesallow more accurate and precise patterning as successive spots of liquidalong a line can be deposited further apart (by a technique such asinkjet printing) allowing a lower volume of liquid to be used, and thusnarrower lines and finer features to be prepared.

This use of the first liquid comprising an activator is particularlybeneficial when using inkjet printing to deposit a material on asubstrate. Many curable liquids have an appropriate viscosity to besuitable to be inkjet printed, giving good print head performance.Suitable viscosities for inkjet printing liquids are typically in therange 1 to 20 cPs at print head operating temperature.

The process may be repeated (optionally with different first liquids andsecond fluids) to build up a multi-layer structure.

The first solid layer preferably includes a first chemical functionalitywhich is at least partially insoluble in the second fluid, as disclosedin our International Application PCT/GB2004/004589. This means that thephysical integrity of the first layer is maintained on contact with thesecond fluid and while the second layer is formed. This has theconsequence of improving adhesion of the second layer with respect tothe substrate surface. The first chemical functionality need not becompletely insoluble in the second fluid, but merely sufficientlyinsoluble to achieve this effect. Thus, the first chemical functionalityonly needs to be sufficiently insoluble in the second fluid to retainthe integrity of the first layer while the second layer is formed.

The second fluid is preferably aqueous, as noted above, so the firstchemical functionality is preferably at least partially insoluble inwater. The first chemical functionality may be present in the firstliquid, and also in the first layer, or may be formed, e.g. bycross-linking, in the first layer from reactants (that are possiblysoluble in the second fluid) in the first liquid. The first chemicalfunctionality is preferably non-ceramic. The first chemicalfunctionality is preferably at least predominantly or fully organicand/or silicon based, comprising at least 50% by weight of organicand/or silicon materials, for improved adhesion to a wide range oforganic substrates such as plastics substrates. The first chemicalfunctionality may absorb the second fluid and swell. The first chemicalfunctionality may be constituted by the reaction product of the curablecomposition, e.g. one or more curable monomers and/or oligomers in thefirst liquid. Such materials may be included in the first liquid andreact to form a polymer in the first layer with appropriate solubilityproperties. The polymer product also has good adhesion to a very widerange of substrates, including metals, glass, ceramics and plasticsmaterials. Thus, the first liquid preferably includes one or moreingredients that constitute or form the first chemical functionality inthe first layer.

Preferably, the components of the first liquid are selected so that thefirst solid layer is permeable to the second fluid when the second fluidis brought into contact with the first solid layer, as disclosed in ourInternational Application PCT/GB2004/004589. We have found that this cansubstantially improve the effective activation/catalytic activity of thefirst solid layer. In particular, the second fluid can penetrate thefirst solid layer, allowing the second fluid to access the activatorwithin the first solid layer. The second layer-forming, reaction canthus take place on, or in close proximity to, the substrate surface,producing the desired second layer of material on the substrate.Furthermore, penetration of the second fluid into the first solid layermay result in the second layer of material intermingling with the firstsolid layer, thereby enhancing adhesion of the second layer of materialto the substrate via the adhered first solid layer and improving throughlayer conductivity (where the second layer is conductive from its topsurface down to the surface of the substrate).

The first layer thus preferably comprises a second chemicalfunctionality which is at least partially soluble, miscible or swellablein the second fluid or permeable to the second fluid, as disclosed inour International Application No. PCT/GB2004/004589. The second fluid ispreferably aqueous, as noted above, so the second chemical functionalityis preferably at least partially soluble or swellable in water orpermeable to water. The second chemical functionality may be present inthe first liquid, and also the first layer, or may be formed in thefirst layer from reactants in the first liquid. Suitable second chemicalfunctionalities are discussed below, and include polyvinylpyrrolidone(PVP), which is soluble in water, and which may be included as aningredient of the first liquid. The second chemical functionality willat least partially dissolve or swell in, or be permeable to, the secondfluid, allowing the fluid to penetrate the first solid layer and contactthe activator. The first chemical functionality retains sufficientintegrity to adhere to the substrate and the second layer, resulting ina “sponge-like” structure. This has the consequence of permittingenhanced access to the activator than would otherwise be the case,allowing the use of lower concentrations of activator, withconsequential cost savings. In particular it is possible to use a firstliquid with a weight ratio of curable composition to activator ofgreater than about 15:1, preferably greater than about 25:1. The abilityto be able to use relatively low proportions of activator in the firstliquid has the benefit of allowing greater freedom in formulation of thefirst liquid, e.g. in terms of properties such as viscosity and solventchoice.

Thus, the first liquid may comprise one or more ingredients whichconstitute or form in the first layer a second chemical functionalitywhich is at least partially soluble, miscible or swelleable in thesecond fluid or permeable to the second fluid. One preferred secondchemical functionality is polyvinylpyrrolidone (PVP), which is solublein water. Alternatives include polyacrylic acid, polyvinyl acetate,polyethylene imine, polyethylene oxide, polyethylene glycol, gelatin orcopolymers thereof. The soluble components may dissolve when the secondfluid is brought into contact with the first solid layer. For example,the polyvinylpyrrolidone will dissolve in contact with an aqueoussolution of metal ion and reducing agent usable to form a conductivemetal region on the first solid layer (see below). Around 5% by weightof polyvinylpyrrolidone in the resulting solid layer is appropriate.

The first liquid could instead (or as well) comprise a water swellablemonomer and/or oligomer such as HEMA (2-hydroxyethyl methacrylate), GMA(glyceryl methacrylate) or NVP (u-vinyl pyrrollidinone). Other monomersand/or oligomers which are themselves swellable in the second fluidand/or are swellable when polymerised could be used instead. This allowsthe second fluid to permeate into the first solid layer, improvingadhesion and allowing access to more activator than just activatorpresent on the surface of the first solid layer.

The first liquid could instead (or as well) comprise a high boilingpoint solvent miscible with the second liquid, with the high boilingpoint solvent remaining in liquid form in the first solid layer. Forexample, NMP (n-methylpyrrolidinone) could be used when the secondliquid is aqueous. This keeps the first layer matrix open allowingpenetration by the second liquid and improving the adhesion of thesecond layer to the first solid layer. Other suitable solvents includeethylene glycol, diethylene glycol or glycerol.

The first liquid could instead (or as well) comprise micro-porousparticles to create a micro-porous film structure. Micro-porousparticles could be organic (e.g. PPVP (poly (polyvinylpyrrolidone))) orinorganic (e.g. silica).

The weight ratio of the first chemical functionality to the secondchemical functionality is preferably greater than about 5:1, morepreferably greater than about 10:1, most preferably greater than about15:1. The use of relatively large amounts of the first chemicalfunctionality results in benefits of improved adhesion to the substratesurface, more rapid curing, durability of the resulting first solidlayer, and improved formulation flexibility for the first liquid.

The first liquid may include a carrier liquid which is volatile andwhich evaporates off, partially or fully, after application to thesubstrate For example, the first liquid may comprise water or(preferably) one or more organic solvents which, in use, are evaporatedoff before the second fluid is brought into contact with the firstlayer. The method in this case may include a pause to allow a volatilecarrier to evaporate before one or both of applying a stimulus (ifapplicable) and bringing the second fluid into contact with the firstlayer. It may be advantageous for some of the carrier liquid to remainin the first solid layer in liquid form, to keep the first layer matrixopen.

Preferably, however, no significant delay between depositing and curingthe first liquid is required, and there is no need for drying orpre-curing steps. This reduces over-wetting of the substrate, whichcauses loss of definition to the image. Preferably the delay betweendeposition and curing is 20 seconds or less. Further, the curing processitself can be achieved very rapidly, typically in less than 1 second,with benefits of control of image quality.

Where the carrier liquid is constituted by liquid monomers/oligomers,substantially all of the constituents of the first liquid may remain inthe first solid layer, albeit possibly in chemically changed form.

As the activator is also included in the first liquid, it will typicallybe trapped within the first layer in a matrix formed, for example, by apolymer. The activator could also be immobilised as part of the matrix,for example, by including the activator on a molecule with a reactivegroup which reacts with monomer or oligomer units. The activator may beinitially inactive, and become active only once the first liquid hasbeen cured, or in response to a stimulus, or when in contact with acomponent of the second fluid.

The invention finds particular application in the production of layersof conductive metal as the second solid layer. Conductive metal layersare typically formed by the reduction of metal ions in a reactioninvolving a catalyst, a metal ion and a reducing agent. A variety ofdifferent techniques may be used, including electroless plating and theprocess disclosed in WO 2004/068389. One reagent of the process,typically the catalyst, is deposited on a substrate (typically by inkjetprinting) in the first layer by the method of the invention, and othernecessary reagents deposited (by inkjet printing, immersion orotherwise) in the second fluid (and possibly in one or more othervehicles) resulting in reaction to form a conductive metal layerconstituting the second solid layer.

In embodiments of the invention where the second layer is a conductivemetal region, formed by the reaction of metal ions and a reducing agent,the activator conveniently comprises a metal or metal-containingmaterial, typically a catalyst or catalyst precursor. Suitable metalsinclude metal colloids or particles, such as colloids or particles ofplatinum, silver, palladium, iridium, bronze, aluminium, gold or copper.Suitable metal-containing materials include salts or complexes of aconductive metal, preferably salts of a transition metal, particularlypalladium, platinum and silver. The salts may be inorganic, such aspalladium chloride, or organic, for example palladium acetate orpalladium propanoate. Preferred organic salts are alkanoates. Thecurrent preferred activator is palladium acetate. Desirably the weightratio of the curable composition to the metal portion of the activatoris greater than about 15:1, preferably greater than about 25:1.

A suitable solvent for the deposition of an organic acid salt of atransition metal, e.g. palladium acetate, include diacetone alcohol, a50/50 mixture of equal parts by weight of diacetone alcohol and methoxypropanol, and a 50/50 mixture of equal parts by weight of toluene andmethoxy propanol. A co-solvent is preferably included to increaseviscosity to suitable levels for inkjet printing. The salt, e.g.palladium acetate, is conveniently present in an amount in the range 1to 3% by weight, preferably about 2% by weight of the deposited liquid.

Where the activator is a catalyst or catalyst precursor, the secondfluid conveniently comprises a solution of a metal ion and a reducingagent, operable to react together, activated by the activator, to form aconductive metal region on the first solid layer. Preferably, thecomposition of the second fluid is such that it does not reactspontaneously, but reacts only once it has been brought into contactwith the activator present in the first solid layer. The second fluidmay further comprise pH-altering reagent such as an acid or a base, toactivate the reducing agent.

The metal ion, the reducing agent and the optional base/acid may bedeposited in two or three separate component solutions which mixtogether on the substrate to form a reaction solution. Further detailsmay be as disclosed in WO 2004/068389.

Where the second layer-forming chemical reaction is to be a reactionbetween metal ions and a reducing agent, to form a conductive metalregion, instead of being a catalyst or catalyst precursor, the activatormay be one or more of metal ions, reducing agent or a pH alteringreagent such as an acid or base. The second fluid will be such that asecond-layer-forming reaction begins when the second fluid is in contactwith the first layer. Where the activator comprises metal ions,typically as metal salts or metal complexes (and perhaps alsoacid/base), the second fluid may comprise reducing agent, possibly withappropriate pH adjusting reagent, e.g. a base in the case offormaldehyde. The second fluid may also contain additional ions of thesame or a different metal. The activator could be metal particles orcolloids. Where the activator comprises a reducing agent (and perhapsalso base or acid), the second fluid will preferably comprise metalions, typically as metal salts or metal complexes. The second fluid maycomprise further reducing agent which may be the same or different tothe first reducing agent. It may be appropriate to use a more powerfulreducing agent such as DMAB (dimethylamineborane) initially followed bya less powerful reducing agent such as formaldehyde which gives a morepure, higher conductivity metal layer. Where the activator comprises pHaltering reagent, the second fluid typically includes metal ions andreducing agent, and optionally further pH altering reagent.

The metal ion may be an ion of any conductive metal, particularly atransition group metal. Preferred conductive metals include copper,nickel, silver, gold, cobalt, a platinum group metal, or an alloy of twoor more of these materials. The conductive metal may includenon-metallic elements, for example, the conductive metal may be nickelphosphorus.

The metal ion is typically in the form of a salt, for example coppersulphate. The metal ion might instead be present in a complex such aswith EDTA (ethylene diamine tetra acetic acid) or cyanide.

Examples of appropriate reducing agents are formaldehyde, glucose ormost other aldehydes, or sodium hypophosphites, or glyoxylic acid orDMAB (dimethylamineborane).

Optionally, the substrate is preheated before the first liquid isdeposited thereon This causes the liquid to dry rapidly and spread less,achieving thinner lines. For example, a Melinex polyester substrate(Melinex is a Trade Mark) may be heated with air at 350° C. for 4seconds using a hot air gun.

Preferably, the first liquid is deposited onto the substrate by inkjetprinting. The second fluid may be deposited on the first layer by inkjetprinting or other techniques. Where the first liquid and/or resultingfirst layer are patterned, the second fluid may be deposited accordingto the same pattern.

As inkjet printing processes are typically digitally controlled,different patterns can be applied using the same apparatus to differentsubstrates. This is particularly important for the production of one-offproducts, customised products, or a series of uniquely identifiableproducts.

The substrate may be selected from a wide range of possibilities,including plastics, ceramics, natural materials, fabrics etc. Inembodiments where the second layer is a conductive metal, suitablesubstrates include plastics materials and fabrics, e.g. in the form ofsheets. A substrate might be a material having thereon electricalcomponents, such as conductive, semi-conductive, resistive, capacitive,inductive, or optical materials, such as liquid crystals, light emittingpolymers or the like. As noted above, the method of the invention neednot involve significant heating and so may be used with a wide range ofsubstrates, including heat-sensitive plastics materials. The method mayinclude the step of depositing one or more of said electrical componentson the substrate, preferably by inkjet printing, prior to forming aconductive metal region on the resulting substrate.

Similarly, the method may further include the step of depositing anelectrical component onto the resulting conductive metal region,building up complex devices. Said further deposition step may also becarried out using inkjet printing technology.

The invention finds particular application in printing of batteries. Abattery may be formed on a substrate by forming two regions of differentconductive metals on a substrate by the method of the invention, andelectrolytically connecting the two regions by way of an electrolyte(which may be inkjet printed), thereby forming an electrochemical cell.A plurality of electrochemical cells may be electrically connected inseries or in parallel thereby increasing the voltage and/or currentavailable. The invention also covers a method of forming a battery byforming two regions of different conductive metals on a substrate by themethod of the invention and electrolytically connecting the two regionsby way of an electrolyte (which may be inkjet printed). The inventionalso extends to a battery formed by the said method.

Thus, the method can be used as one stage in the fabrication ofelectrical items. It is particularly appropriate for use inmanufacturing electrical items which involve complex patterns, such asdisplays which include complex patterns of pixels. Other applicationsinclude the fabrication of aerials or antenna for car radios, mobilephones, and/or satellite navigation systems; radio frequency shieldingdevices; edge connectors, contact and bus connectors for circuit boards;radio frequency identification tags (RFID tags); conductive tracks forprinted circuit boards, including flexible printed circuit boards; smarttextiles, such as those including electrical circuits; decorations;vehicle windscreen heaters; components of batteries and/or fuel cells;ceramic components; transformers and inductive power supplies,particularly in miniaturised form; security devices; printed circuitboard components, such as capacitors and conductors; membrane keyboards,particularly their electrical contacts; disposable, low cost electronicitems; electroluminescent disposable displays; biosensors, mechanicalsensors, chemical and electrochemical sensors.

The method also finds application in producing an electrical connectionbetween two components in or for a circuit.

The method may also be used to produce decorative features.

The method may include the further step of forming an additional metallayer onto a conductive metal region constituted by the second layer,e.g. by electrolytic or electroless plating or by immersionmetallisation.

Where the first liquid, and/or the second liquid, are inkjet printed,the respective liquids should fulfil the specific requirements of inkjetprinting inks as regards viscosity, surface tension, conductivity, pH,filtration, particle size and ageing stability. One or more humectantsmay be added to one or more component solutions to reduce evaporation.The particular values of these properties which are required aredifferent for different inkjet technologies and suitable componentsolutions fulfilling these properties can readily be devised for aspecific application by one skilled in the art.

The method also extends to an article prepared according to the methodof the invention.

According to a further aspect of the present invention there is provideda liquid comprising a curable layer-forming composition for forming afirst solid layer on the surface of a substrate, the liquid comprisingan activator suitable for activating a second layer-forming chemicalreaction, and one or more chemical components which are capable ofundergoing a chemical reaction (typically responsive to a stimulus)causing the liquid to harden.

The invention also covers the activator liquid in combination with asecond fluid.

Preferably, the one or more chemical components comprise monomers and/oroligomers which can polymerise, forming a solid first layer.

The activator is preferably a catalyst. However, the activator couldcomprise a chemical species which can activate the second solid layerforming chemical reaction but which is consumed or reacts in theprocess.

The activator may also comprise a reagent, or a plurality of reagentswhich, when brought into contact with a second liquid comprisingcomponents (preferably other components) of a second layer-formingchemical reaction, undergo a chemical reaction leading to formation of asecond layer on the first solid layer.

Suitable solvents for the deposition of an organic acid salt of atransition metal include diacetone alcohol, mixtures of equal amounts byweight of diacetone alcohol and methoxypropanol, and mixtures of equalamounts by weight of toluene and methoxypropanol. A co-solvent ispreferably included to increase viscosity to suitable levels for inkjetprinting. Preferably the organic acid salt of a transition metalconstitutes 1-3% by weight of palladium acetate, most preferably 2% byweight of the deposited liquid. An equivalent concentration of anotherorganic acid salt of a transition metal can be employed.

Preferred features of the layer-forming activator solution are asdiscussed above.

In a further aspect of the present invention there is provided a methodof forming on the surface of a substrate a first layer which is suitablefor activating a second solid layer-forming chemical reaction thereon,the method comprising the steps of: applying a curable liquid to thesurface of the substrate, the curable liquid comprising an activator fora layer-forming chemical reaction; and curing the curable liquid,thereby forming a first solid layer on the surface of the substrate,capable of activating a second solid layer-forming chemical reaction.

The invention also extends to a method of forming a solid layer on asubstrate, comprising the steps of: applying a curable liquid to thesurface of the substrate, the curable liquid comprising an activator fora layer-forming chemical reaction; curing the curable liquid, therebyforming a first solid layer on the surface of the substrate, capable ofactivating a second solid-layer-forming chemical reaction thereon; andbringing into contact with the first solid layer a second liquidcomprising components of a second solid-layer-forming chemical reaction,activated by the activator, thereby causing a second solid layer to beformed on the first solid layer.

The invention will be further described, by way of illustration, in thefollowing Examples. In the Examples all percentages are percentages byweight unless otherwise specified.

EXAMPLE 1

UV curable catalyst formulations referred to as ALF 116 and ALF 117 wereprepared according to the formulation shown in Table 1 below. Themonomers, oligomers and initiators used are already known from therelated field of WV curable inkjet inks to have excellent curingproperties and adhesion to plastic substrates. These formulationscontain some solvent (diacetone alcohol and methoxy propanol) acting asa carrier liquid in which the palladium acetate catalyst is soluble. Thesolvent was allowed to evaporate off after application of theformulation to a Melinex (Melinex is a Trade Mark) polyester substratesurface by inkjet printing using an XJ500/180 print head from Xaar, UK.The inks were then cured by the application of UV which began a curingprocedure in which the monomer and oligomer components polymerised.

UV Curable Catalyst Formulations Figures are Percentages by Weight

TABLE 1 Materials ALF 116 ALF 117 Palladium acetate 1.25 0.94 PVP K30 —2.5 Diacetone alcohol (DAA) 24.38 23.28 Methoxy propanol 24.37 23.28Actilane 505 5 5 DPHA 1.5 1.5 Irgacure 1700 3.25 3.25 Irgacure 819 1.251.25 DPGDA 39 39

PVP K30 is a grade of polyvinyl pyrrolidinone supplied by ISP, Tadworth,UK. Actilane 505 is a UV-curable reactive tetrafunctional polyesteracrylate oligomer supplied by Akzo Nobel UV Resins, Manchester, UK. DPHAis dipentaerythritol hexacrylate, a IV-curable hexafunctional monomer,supplied by UCB, Dragenbos, Belgium. Igracure 819 and Igracure 1700 areUV photo-initiators supplied by Ciba Speciality Chemicals, Macclesfield,UK—Irgacure is a Trade Mark. DPGDA is dipropylene glycol diacrylate, aUV-curable reactive diluent monomer supplied by UCB, Dragenbos, Belgium.The monomers and oligomers are in liquid form. Diacetone alcohol andmethoxy propanol are solvents for the palladium acetate.

PVP constitutes a water soluble (second) chemical functionality. Themonomers and oligomers, Actilane 505, DPHA and DPGDA, react to form apolymer that constitutes a water insoluble (first) chemicalfunctionality.

ALF 116 cured well (with a line speed of 40 metres/minute) to give atough scratch resistant film. However, when a copper layer formingsolution (consisting of Enplate 872A (30% w/w), Enplate 872B (30% w/w),Enplate 872C (10% w/w), t-butanol (5% w/w), ethylene glycol (20% w/w)and polyethylene glycol 1500 (5% w/w) was applied to the film, no copperwas deposited. We believe that this is due to the smooth, impervioussurface of the cured film, which seals the catalyst into a plastic layerand prevents it from coming into contact with the copper-layer formingsolution.

Enplate 872A, 872B and 872C are copper plating solutions, available fromEnthone-OMI of Woking, UK. Enplate 872A contains copper sulphate.Enplate 872B contains a cyanide complexing agent and formaldehyde.Enplate 872C contains sodium hydroxide. (Enplate is a Trade Mark.)Enplate 872 A, B and C are in common use as component solutions forelectroless copper plating. Ethylene glycol is present as a humectantand acts to lower surface tension. T-butanol is a cosolvent whichreduces surface tension and increases wetting. Polyethylene glycol-1500functions as a humectant.

In contrast, ALF 117 includes a small amount (5% by weight of driedfilm) of polyvinylpyrrolidone, which was added to the formulation withthe aim that it would dissolve out of the cured layer or swell ormaintain permeability upon the subsequent addition of the aqueouscopper-layer forming solution, and therefore expose the catalytic sites.

As with ALF 116, this again cured very well at 40 metres/minute and thistime deposited copper (at a calculated 100 nm/minute).

Drying the substrate at 60° C. for 24 hours resulted in a materialhaving good scratch resistance properties, as good as the scratchresistance of the best catalyst formulation we know for direct bondingof a copper-layer to a plastic substrate.

This work indicated that in order to maintain the activity of thecatalyst it was necessary to have some form of water solubility,swellability, or other means to enable the second liquid to penetratethe first layer.

EXAMPLE 2

Three further formulations referred to as ALF 120, ALF 121, and ALF 124were prepared as summarised in Table 2 below. Each of these is a variantof ALF 117 from Table 1.

UV-Curable Catalyst Formulations

TABLE 2 ALF 120 ALF 121 ALF 124 Palladium acetate 2 2 2 DPGDA 76 48 48DPHA 3 3 3 Actilane 505 10 10 10 Irgacure 1700 6.5 6.5 6.5 Irgacure 8192.5 2.5 2.5 Diacetone alcohol — 12.75 14 Methoxy propanol — 12.75 14 PVPK30 — 2.5 —

The formulations ALF 120, ALP 121 and ALF 124 were applied to a Melinexpolyester substrate, as described above in Example 1.

These inks were cured using a Fusion UV 500 Watt lamp fitted with an Hbulb (fusion is a Trade Mark), in a single pass at 10 metres/minute.After curing the inks were treated with DMAB (dimethylamineborane)solution followed by a copper-layer forming solution consisting ofEnplate 872A (30% w/w), Enplate 872B (30% w/w), Enplate 872C (10% w/w),t-butanol (5% w/w), ethylene glycol (20% w/w) and polyethylene glycol1500 (5% w/w). No copper was deposited on ALP 120 or ALF 124. However, agood uniform layer of copper was deposited on ALF 121. This copper layerwas found to have good conductivity, and good adhesion to the underlyingsubstrate. Since no copper was deposited on ALF 120 or ALF 124 thisprovides further evidence that the PVP material is responsible formaintaining the activity of the catalyst, and that it is likely thatthis occurs via the water solubility mechanism proposed above.

EXAMPLE 3

ALF 121 was then modified further to give an ink with good propertiesfor deposition by inkjet printing. Two such inks, referred to as ALF 125and ALF 126b, are shown in Table 3 below.

Jettable UV Ink Formulations

TABLE 3 ALF 125 ALF 126b Palladium acetate 2 2 Irgacure 1700 3.25 3.25Irgacure 819 1.25 1.25 DPGDA 61 48 DPHA — 3 Actilane 505 — 10 Diacetonealcohol 15 15 Methoxy propanol 15 15 PVP K30 2.5 2.5 viscosity, cPs (25°C.) 9.59 11.2

ALF 125 and ALF 126b both showed good inkjet printing properties using aXaarJet 128-200 print head (available from Xaar of Cambridge, England)and both gave good quality copper deposition on a Melinex polyestersubstrate following the procedure described above in Examples 1 and 2.However, when making thicker copper samples of greater than 200 nmthickness, ALF125 blistered much more easily than ALF 126b.

This is thought to be because ALF 126b contains higher functionalitymaterials (Actilane 505 is tetrafunctional, DPHA is hexafunctional) andso is more highly cross-linked and therefore forms a stronger, morerobust film with better adhesion to the substrate.

Based on these results, it is also thought that it should be possible toreplace the PVP with a water-swellable monomer such as HEMA(2-hydroxyethyl methacrylate), GMA (glyceryl methacrylate) or n (n-vinylpyrrolidinone). Alternatively, a high boiling point water misciblesolvent such as NMP (n-methylpyrrolidinone), ethylene glycol, diethyleneglycol or glycerol could be used to keep the UV-cured layer open, and toallow penetration by the copper solution. Alternatively, a micro-porousfilm structure could be prepared by the use of micro-porous particles,such as silica (inorganic) or PPVP (poly polyvinyl pyrrolidinone)particles (organic).

EXAMPLE 4

ALF 126b was then modified further to give a WV-curable catalyst inkwith optimised performance, known as ALF 126f. This was used to deposita conductive copper layer on a Melinex (Melinex is a Trade Mark)polyester substrate. The composition of ALF 126f was as follows:

ALF 126f Jettable UV Ink Formulation

TABLE 4 ALF 126f Palladium acetate 2 Irgacure 1700 3.25 Irgacure 8191.25 DPGDA 30.5 DPHA 3 Actilane 505 10 Diacetone alcohol 47.5 PVP K302.5 Viscosity, cPs (25° C.) 17.6

This fluid was printed with a XJ500/180 print head (available from Xaarof Cambridge, England) at 180×250 dpi. The samples were then cured undera Fusion 500 Watt H-bulb, in 4 passes of 20 metres/min each, resultingin formation of the first layer. For a line printed using a single jet,the thickness was measured at about 500 nm. For larger area coverage thelayer thickness will increase, possibly up to the theoretical maximumfor this printing resolution of 2.9 microns. The samples were submergedin a chemical bath containing a solution of 1.6% dimethylamineborane(DMAB) in deionised water, and processed at 40±2° C. for 2 minutes,followed by a deionised water rinse, and drying. This treatment reducedthe palladium acetate to palladium metal, thus activating the catalyst.The samples were then treated with a copper layer forming solution, thesolution consisting of 75% deionised water and ENPLATE Cu 872A, ENPLATECu 872B, and ENPLATE Cu 872C in the weight ratio 3:3:1, respectively.The samples were immersed in the copper layer forming solution underagitation for 2 minutes, while held at 45±2C in a temperature controlledbath.

As with ALF 126b, ALF 126f showed good inkjet printing properties andgave good quality copper deposition.

EXAMPLE 5

ALF 126f ink was coated onto a Melinex 339 (Dupont Teijin Films)polyester substrate using a 12 μm drawdown bar. The liquid film was thenexposed to UV light through apertures patterned in a 25 micron aluminiumfoil. The UV light source was a Fusion systems F500 using an H bulb,giving a total UV dose of 0.70 J/cm². The exposed areas of the filmcured and solidified. The unexposed areas remained liquid and wereeasily washed away using ethanol. A further four passes under the UVlamp ensured fall curing.

The films were then immersed in a 1.6% solution of DMAB at 40° C. for 2mins, washed and then placed in an electroless copper plating bath(Enplate Cu 872A, Enplate Cu 872B and Enplate Cu 872C in the weightratio 3:3:1, respectively) at 45° C. for 2 minutes and then rinsed againin deionised water. Copper metal was plated onto the exposed regionswhereas the unexposed areas remained uncoated.

EXAMPLE 6 Direct Laser Writing

Structures were directly written using the process of direct laserwriting. Liquid films of ALF 126f ink of between 12 microns and 24microns were prepared on a Melinex 339 polyester substrate (Melinex is atrademark of Dupont Teijin Films) using the draw-down method. The liquidfilms were immediately fed into an Orbotech DP100 SL Direct laser writesystem (Orbotech is a Trade Mark). This system uses a 4 W Paladin(Paladin is a Trade Mark) diode pumped solid state laser (Coherent Ltd)operating at 355 nm.

Patterns were produced using energy dosed from 20 mJ up to 100 mJ in anatmosphere of nitrogen gas (although this is not essential). The uncuredareas were washed away using ethanol. The samples were then immersed ina 1.6% solution of DMAB for 2 minutes, rinsed in DI water and thenplated by immersion in Enplate copper plating solution (Enplate Cu872A,Enplate Cu 872B and Enplate 872C in the weight ratio 3:3:1,respectively) for 2 minutes at 45° C. This resulted in well adheredcopper features as fine as 20 microns.

1. A method of forming, on the surface of a substrate, a first solidlayer which is capable of activating a chemical reaction to form asecond layer thereon, the method comprising bringing into contact thesubstrate surface and a first liquid comprising a curable compositionand an activator for said second layer-forming chemical reaction; andcuring the curable composition to increase adhesion of the material tothe surface of the substrate, thereby forming a first solid layer,capable of activating said second layer-forming chemical reaction aftercontact with a second fluid.
 2. A method according to claim 1, furthercomprising bringing into contact the first solid layer and the secondfluid that comprises one or more reagents for chemical reaction,activated by the activator, to form the second layer.
 3. A methodaccording to claim 2, wherein the second layer comprises a conductivemetal layer.
 4. A method according to claim 3, wherein the secondlayer-forming chemical reaction is a reaction between metal ions and areducing agent, to form a conductive metal region, and the activatorcomprises one or more of catalyst metal ions, reducing agent or apH-altering reagent.
 5. A method according to claim 1, wherein thecurable composition comprises one or more monomers and/or oligomerswhich can polymerise and/or cross-link in use, thereby hardening andforming a solid layer.
 6. A method according to claim 5, wherein thecurable composition comprises one or more acrylates or methacrylates. 7.A method according to claim 5 or 6, wherein the curable compositionincludes a proportion of monomers and/or oligomers having at least 3cross-linkable functional groups.
 8. A method according to claim 1,wherein the first liquid is such that the first solid layer includes afirst chemical functionality that is at least partially insoluble in thesecond fluid.
 9. A method according to claim 1, wherein the first liquidis such that the first solid layer is permeable to the second fluid. 10.A method according to claim 9, wherein the first solid layer includes asecond chemical functionality which is at least partially soluble,miscible or swellable in the second fluid, or otherwise penetrable bythe second fluid.
 11. A method according to claims 8 and 10, wherein theweight ratio of the first chemical functionality to the second chemicalfunctionality is greater than about 5:1, preferably greater than about10:1, more preferably greater than about 15:1.
 12. A method according toclaim 1, wherein the weight ratio of the curable composition toactivator in the first liquid is greater than about 15:1, preferablygreater than about 25:1.
 13. A method according to claim 1, wherein thefirst liquid is brought into contact with the substrate surface by aprinting process, preferably a non-contact digital printing process. 14.A method according to claim 1, wherein the first solid layer is formedon the substrate surface according to a pattern.
 15. A method accordingto claim 14, wherein the first liquid is deposited onto the substratesurface according to a pattern by digital inkjet printing.
 16. A methodaccording to claim 14, wherein the curable liquid is applied extensivelyto the substrate surface and selectively cured according to a pattern.17. A method according to claim 1, wherein the second fluid is depositedon the first solid layer by inkjet printing.
 18. A method according toclaim 1, wherein the curable composition is curable in response to astimulus.
 19. A method according to claim 18, wherein the curablecomposition is curable in response to ultraviolet radiation.
 20. Amethod according to claim 1, wherein the activator comprises a metal ormetal-containing material
 21. A method according to claim 20, whereinthe weight ratio of the curable composition to the metal portion of theactivator is greater than about 15:1, preferably greater than about25:1.
 22. A method according to claim 20 or 21, wherein the activatorcomprises a catalyst.
 23. A method of fabricating an electrical itemcomprising the method of any one of claim
 1. 24. A method according toclaim 1, for use in producing a battery.
 25. A method according to claim1, for use in producing an electrical connection between two componentsof a circuit.
 26. A method according to claim 1, for use in producing adecorative feature.
 27. An article prepared according to the method ofclaim
 1. 28. A liquid comprising a curable layer-forming composition forforming a first solid layer on the surface of a substrate, the liquidcomprising an activator suitable for activating a second layer-formingchemical reaction, and a curable composition capable of being cured toincrease adhesion of the material to the surface of the substrate and toform a first solid layer adhered to a substrate and capable ofactivating said second layer-forming chemical reaction.